Before I started testing I already knew that the ad impressions would go down. I tested asynchronous ads before, but not very extensively, so I need some precise numbers for my site.

As you can see above, the results are not pretty. Impressions went down 50%. Most sites usually have one unit that is performing really well and it usually sits above the fold. If you start using asynchronous ads, people can scan your site more quickly and may ignore ads that sit above the fold. In any case, the numbers don’t lie. However, ad impressions alone are not very conclusive.

Reason 2: Bounce Rate Does Not Improve Significantly

If I were to use asynchronous ads, it should at least improve my bounce rate so I can get higher rankings for some time. So I decided to look at the bounce rate:

As you can see the bounce rate only improved during one hour and that may just be a fluctuation. In general the bounce rate did not improve or was even a couple percentage points worse than before.

Another reason not to use them is that the user experience does not improve. On the contrary, when I visit a site with asynchronous ads I find myself waiting for this page to be fully loaded (ads are also part of a page), while synchronous ads are already loading when I first open the page making it easier to quickly scan a page. I find it somewhat silly that Google is using the time it takes to fully load a site as a ranking factor, instead they should look closer at the time it takes until the first rendering takes place, which is really more about “first-byte” time and how well your server is responding.

Reason 3: Revenue Drops By 70-80%

During my tests with asynchronous ads, revenue dropped 70-80%. It’s possible that the Adsense bot may have to fully crawl your site again and that’s why the numbers were so bad. This is not so great for large sites, as it could take a long time. There’s obviously a correlation between ad unit impressions and revenue, so it only makes sense that the revenue went down, but I didn’t expect such a huge drop:

This really shows that Async ads are not ready for implementation just yet. At least not on my sites. I will stay away from those for some time to come or until I have figured out why they are performing so badly for me. Obviously, there can be other reasons involved, like a bad server response time during my tests, but I tested very carefully and made sure the server was responsive at all times.

Oliver is the founder of webmaster.net and wants to help other webmasters to grow and optimize their sites. He started creating websites in 2006, turned it into his profession by 2010 and has been working on his websites and services ever since. Connect with him on LinkedIn for frequent webmaster updates.

I went one step further and added another above the fold ad unit and it actually increased the CTR on other ad units because it delays the ad loading speed. I believe users keep waiting until a site is fully loaded including ads, that may explain the CTR increase.